A 1500-μm-diameter silicon/silicon nitride 3D scan mirror has been built using MEMS technology. It is capable of static and dynamic beam scanning achieved with a bi-axial gimbal. A gold-coated deformable membrane at the center of the device provides both focus control (z-axis) and spherical aberration correction. This architecture is able to move the focus of a laser beam throughout a three-dimensional space with a single optical surface, and is referred as a 3D scan mirror. This mirror will be incorporated into a miniature confocal laser scanning microscope for biomedical in-situ imaging applications. In this paper we describe the 3D scan mirror design, fabrication and characterization as well as its target application.